Method for making a sound transducer integrated into an acoustic signal generating card

ABSTRACT

The invention relates to a sound transducer in fluoride polyvinylidene (FPVD), its process of manufacture and integration into a card producing acoustic signals transmittable by telephone route. The process is chiefly characterized in that it consists of making ( 10 ) dual surface metallization strips distributed over the entire width of a ribbon in FPVD of great length and of very narrow thickness, cutting ( 11 ) each metallization strip into a unit film, fixing ( 12 ) a portion of film onto a pre-determined site of an interconnection array made on the rear surface of the card, cutting away excess film, then placing the film portion under stress ( 13 ), in such manner that it may emit acoustic signals when voltage is applied to it. 
     This process is highly useful for the manufacture of acoustic signal producing cards of very narrow thickness and low cost price.

This invention relates to a sound transducer and more particularly toits process of manufacture and its integration into a card of narrowthickness able to produce acoustic signals.

Said card can be used to transfer confidential information in securemanner, towards a server for example, via a telephone line.

Acoustic signals are produced following the principle of data coding bya pair of frequencies of 697 to 1633 Hz and are better known by theirEnglish term Dual Tone Modulation Frequency (DTMF). In telephony theseDTMF signals are used for numbering, code transmission etc.

Today it is known how to fabricate sound transducers in ceramic having athickness of approximately 0.3 mm, for their insertion into cards ofnarrow thickness, that is to say approximately 0.8 mm thick. However,such transducers in ceramic are very expensive and considerably increasecard cost price.

Other materials are therefore being researched with a view to producinglow cost sound transducers. In particular, the use of a material influoride polyvinylidene (FPVD) has already been considered. FPVD is anadvantageous material since it is cheap and also allows maintainedamplitude differences existing between the two frequencies whichdetermine DTMF signals.

However, up until now, it has proved impossible to produce a very thinFPVD transducer for its insertion into a card of conventional format,having a thickness of approximately 0.8 mm. The FPVD sound transducerscurrently produced all comprise two FPVD films that are electricallyconnected and placed under stress. These films are housed in a framewhose thickness lies between 0.8 and 1 mm. Each transducer thus formedforms a unit part which must then be fixed in a card, with contactsre-connected by means of conductor wires.

The assembly of such transducer in a card therefore requires meticulouscare and is fastidious and time consuming. Also, the card is too thick,more than the normalized thickness for electronic cards since it isbetween 1.5 and 2 mm. Finally, the sound transducer is fragile since itcannot resist against stresses due to bending of the card in which it isinserted.

The present invention remedies all these drawbacks since it describes aprocess for manufacturing a sound transducer in FPVD and integrating thelatter into a card of conventional format for electronic cards inaccordance with standard ISO 78.16-12 and whose thickness is reduced toapproximately 0.8 mm. This card can be used to produce acoustic signalstransmittal by telephone route. On its rear surface it carries aninterconnection array. The process of the invention is particularlycharacterized in that it consists of:

making dual surface metallization strips, forming electrodes,distributed over the entire width of a ribbon in FPVD of great lengthand of very narrow thickness,

cutting off each metallization strip to form unit films of great length,

fixing a portion of the film onto a predetermined site of theinterconnection array on the rear surface of the card and cutting offexcess film, and

placing the film portion under stress in such manner that it can emitacoustic signals when voltage is applied to it.

A further object of the invention concerns a sound transducer in FPVDintegrated into a card producing acoustic signals transmittable bytelephone route, whose rear surface carries an interconnection array,characterized in that it comprises:

grooves parallel to one another made on the rear surface of the card,

a portion of film in FPVD, of very narrow thickness, carrying twoelectrodes, one lower and one upper, connected to the interconnectionarray of the card, and

a stress part whose lower side comprises notches parallel to one anotherable to position themselves opposite the grooves and to press upon theportion of film so as to impart indentations upon it.

The sound transducer of the present invention is made within the cardproducing DTMF signals. Consequently, the transducer no longer has theappearance of a unit part inserted into the card but forms an integralpart of the card. On this account, its mechanical resistance to stressesdue to bending of the card for example is largely improved. Also, theintegration of the transducer into the card is simple to perform bygluing.

Other particularities and advantages of the invention will be apparenton reading the description given by way of illustration which isnon-restrictive and refers to the appended figures which represent:

FIG. 1, an organization diagram illustrating the stages of the processof the invention,

FIG. 2, metallization strips on a ribbon of great length;

FIGS. 3A to 3E, diagrams of a card of narrow thickness during theintegration of a sound transducer of the invention,

FIG. 4, a cross section view A—A of the sound transducer of FIG. 3D.

One embodiment of a process in accordance with the invention issummarized in the organization diagram of FIG. 1. Such process consists,in an initial stage 10, of making dual surface metallization strips on aribbon in FPVD of great length and of very narrow thickness. Thesemetallization strips are distributed over the entire width of the ribbonand their width corresponds to that of the transducer to be produced.The manner in which these metallizations are made is explained below.During the next stage 11, each metallization strip is cut off to form aunit film of great length that is entirely metallized on its twosurfaces, lower and upper. The metallizations therefore form twoelectrodes, one lower, one upper, on the unit film. In parallel tostages 10 and 11, passive and active electronic components are fixed andwired onto the rear surface of a card. Subsequently, during stage 12,one portion of the unit film is fixed to the rear surface of the cardand more precisely its two electrodes are connected to aninterconnection array made on this rear surface. The fixing of the filmportion is described below. Finally, stage 13 consists of placing theportion of film under stress so that it may emit acoustic signals whenvoltage is applied to it.

All these stages of the process will be better understood with referenceto FIGS. 2 to 4.

FIG. 2 illustrates one embodiment of producing metallization strips 22on ribbon 20 of great length and of very narrow thickness. Ribbon 20 isin fluoride polyvinylidine (FPVD) and is in the form of a roll.Advantageously, the molecular dipoles of the FPVD are previouslyoriented, in permanent manner, using a method well known to thoseskilled in the art. The roll is gradually unrolled and carried, atconstant speed, into a depositing chamber 21.

Metallization strips 22 are then made on the lower and upper surfaces ofthis ribbon, using an evaporation process for example, in chamber 21.

In order to achieve uniform strips of constant width, masks, not shownin FIG. 2, are placed in evaporation chamber 21. The small, remainingnon-metallized strips, of identical width to that of the masks placed inthe evaporation chamber, that is to say having a width of approximately10 mm, advantageously form cutting axes 23. These cutting axes 23 areused to cut each metallization strip 22 into a unit film of great lengthand very narrow thickness, of between 9 and 12 μm.

Also, cutting axes 23, non-metallized, are sufficiently wide to avoidany formation of a side short-circuit between the two metallizedsurfaces of a strip during cutting.

FIGS. 3A to 3E illustrate the finishing stages of a transducer made inaccordance with the process of FIG. 1 and, more particularly, theillustrate the manner in which such transducer is integrated into a cardof narrow thickness. Therefore, FIG. 3A shows the rear surface 100 of acard producing acoustic signals. The upper part of this rear surface 100carries an interconnection array 110 on which are fixed the requiredelectric components for the card to operate, namely: a micromodule 140,a circuit 130 producing acoustic signals, a resonator 160, a battery 150and other passive components. These electronic components are fixed bygluing, for example, using an anisotropic conductor adhesive.

Also, grooves 120 are made on rear surface 100 at the site of the soundtransducer. These grooves are oriented parallel to one another widthwisein relation to the card, for example, and are made between two contactpoints 112, 113 of interconnection array 110. These two contact points112, 113 are provided for connection of the upper and lower electrodesof a portion of unit film such as described above. The width of eachgroove is preferably between 2 mm and 3 mm for a transducer whose lengthlies between 27 and 35 mm. Also, the depth of each groove is in theregion of 0.19 mm for a rear surface with a thickness of approximately0.2 mm. According to one variant of embodiment, the grooves may also bedirected lengthwise over the card parallel to each other. In this case,the fabrication of the integrated transducer of the invention isidentical, a rotation of 90° C. simply exists in relation to thedescription already given. Rear surface 100 is preferably made in amaterial having good mechanical rigidity such as epoxy glass forexample.

Unit film 22 in FPVD, metallized on its two surfaces, is subsequentlyplaced in position, in such manner as to cover grooves 120 as shown inFIG. 3B. For this purpose, the unit film is previously made taut andthen glued, first to one end position, onto a first contact point 112 oninterconnection array 110. Gluing is made using an anisotropic conductoradhesive 27 in order to connect the lower electrode of film 22electrically to contact point 112. The film is also glued on rearsurface 100 of the card, to a second end position using ordinary glue 26of conventional type. Film 22 is then cut along cutting axis 24 in suchmanner as to cut away excess film and maintain solely a portion of film25 fixed, at both its ends, onto rear surface 100 of the card.

Caution must however be taken when cutting the film to avoid any sideshort-circuits likely to form between the lower and upper electrodes offilm portion 25. Such precaution consists in particular of using veryslow cutting procedure without pressing upon film portion 25.

Preferably, film portion 25, metallized either side, is fixed to rearsurface 100 in such manner that the molecular dipoles are orientedparallel to the longitudinal side of rear surface 100 of the card.

Also, the thickness of this film portion 25 is very narrow since itadvantageously lies between 9 and 12 μm.

In a following stage, illustrated in FIG. 3C, a second electricconnection is made between unit film portion 25 and interconnectionarray 110. The upper electrode of film portion 25 is connected to thesecond contact point 113 of interconnection array 110, located near thesecond end position of the film portion. For this purpose a metal wafer28 is fixed on the upper electrode of film portion 25 and on secondcontact point 113 using an anisotropic conductor adhesive.

Film portion 25 having been fixed onto the rear surface of the card, itmust subsequently be placed under stress so that it may emit soundsignals when voltage is applied to it. A stress part 170 of rectangularshape able to cover the entire surface of film portion 25 is then made.

Advantageously, notches 171 are made on the lower side of stress part170. These notches 171 are parallel to one another and orientedwidthwise in relation to part 170. Therefore when stress part 170 ispositioned, notches 171 come to place themselves opposite grooves 120 ofrear surface 100 and exert pressure on film portion 25 so as to impartindentations upon it.

Since the molecular dipoles of the FPVD are oriented, the response offilm portion 25 becomes anisotropic when the latter is placed understress. For this purpose, it is important to fix film portion 25 in suchmanner that its molecular dipoles are perpendicular to grooves 120. Itis when stress is applied in a manner that is perpendicular to theorientation of the molecular dipoles of the FPVD that the soundtransducer made in accordance with the present invention best operates.This is why, since grooves 120 are made widthwise in relation to thecard, film portion 25 is fixed so that its molecular dipoles areoriented parallel to the longitudinal side of the card. In the variantdescribed above, when the grooves are made lengthwise in relation to thecard, film portion 25 and stress part 170 need only be rotated through90°.

Preferably the transducer thus produced and shown in its entirety inFIG. 3D, is of rectangular shape, with a width of between 25 and 30 mmand a length of between 27 and 35 mm.

Also, when the transducer is placed in operation, another problem wasraised since, according to the theoretical teaching of the prior art, avoltage of roughly one hundred volts would need to be applied to theterminals of the transducer of the invention, in order to obtainresponse similar to that of a conventional ceramic transducer, to whoseterminals a voltage of three to six volts is applied. Yet, surprisingly,it was ascertained that a voltage of twelve volts applied to theterminals of the transducer produced in accordance with the presentinvention allows correct response to the obtained.

Rear surface 100 of the card is subsequently covered by a front surface180 as illustrated in FIG. 3E, in whose lower side is made a largecavity 181 able to support the electronic components fixed on the rearsurface. Also a pad, not shown in FIG. 3E, placed in cavity 182 of frontsurface 180, is used to actuate a system triggering circuit 130 whichproduces acoustic signals. With this pad it is possible to by passcontact points 111 in interdigital lines, belonging to interconnectionarray 110, in such manner as to establish contact able to triggercircuit 130.

According to one variant it is possible to make the stress part directlyon the lower side of front surface 180. In this way it forms an integralpart of the front surface of the card. Also this further reduces thethickness of the card.

FIG. 4 shows a section diagram A—A of the sound transducer of FIG. 3D.Rear surface 100 is shaded. The depth of grooves 120 is approximately0.19 mm and their width is between 2 and 3 mm. At one first end, on theleft in FIG. 4, the lower electrode of film portion 25 in FPVD iselectrically connected to the first contact point 112 of theinterconnection array, by means of an anisotropic conductor adhesive 27.At a second end, on the right in FIG. 4, the lower electrode of filmportion 25 is fixed to rear surface 100 by gluing, using ordinary glue26, and the upper electrode is electrically connected to second contactpoint 113 of the interconnection array, not shown in FIG. 4, via a metalwafer 28 fixed by gluing using an anisotropic conductor adhesive 27.

Stress part 170 with its notches 171 has a thickness which preferablylies between 0.3 and 0.4 mm. Notches 171 are positioned opposite grooves120 made on rear surface 100 and press upon film portion 25 so as toimpart indentations upon it. Also grooves 120, advantageously, formtypes of small cavities in which the film portion in FPVD, placed understress, can vibrate when voltage is applied to it.

According a variant of embodiment, it is also possible to make outletholes, not shown in FIG. 4, distributed in regular fashion along grooves120 of rear surface 100 in such manner that they facilitate emission ofacoustic signals.

What is claimed is:
 1. Sound transducer in fluoride polyvinylidine(FPVD) integrated in a card producing acoustic signals transmittable bytelephone route, whose rear surface (100) carries an interconnectionarray (110), characterized in that it comprises: grooves (120) parallelto one another, carried by rear surface (100) of the card, a filmportion (25) in FPVD, of very narrow thickness, supporting twoelectrodes, one lower, one upper, which are connected to interconnectionarray (110) of the card, and a stress part (170) whose lower sidecomprises notches (171) parallel to one another, able to positionthemselves opposite grooves (120) and to press upon film portion (25) toimpart indentations upon it, and the thickness of stress part (170)fitted with notches (171) being between 0.3 and 0.4 mm.
 2. Transducer inaccordance with claim 1, characterized in that the thickness of filmportion (25) lies between 9 and 12 μm.
 3. Transducer in accordance withclaims 1, to 2, characterized in that it is of rectangular shape, havinga width of between 25 and 30 mm and a length of between 27 and 35 mm. 4.Sound transducer in fluoride polyvinylidine (FPVD) integrated in a cardproducing acoustic signals transmittable by telephone route, whose rearsurface (100) carries an interconnection array (110), characterized inthat it comprises: grooves (120) parallel to one another, carried byrear surface (100) of the card, a film portion (25) in FPVD, of verynarrow thickness, supporting two electrodes, one lower, one upper, whichare connected to interconnection array (110) of the card, and a stresspart (170) whose lower side comprises notches (171) parallel to oneanother, able to position themselves opposite grooves (120) and to pressupon film portion (25) to impart indentations upon it, and stress part(170) forms an integral part of front surface (180) of the card. 5.Transducer in accordance with claim 4, characterized in that thethickness of stress part (170) fitted with notches (171) is between 0.3and 0.4 mm.
 6. Transducer in accordance with any of claims 1, or 2, or5, or 4, characterized in that grooves (120) have a depth ofapproximately 0.19 mm.
 7. Transducer in accordance with any of claims 5or 4 characterized in that the thickness of film portion (25) liesbetween 9 and 12 μπ.